**Spoiler Alert** the final battle is with Naraku and he has 10,000 HP...overkill X.X
The best way I found to beat him was to train at Hount Houoh, and find your way to the monk house and replinish everyones HP...rinse and repeat ^^ you'll get about 300-400 EXP each and about 600-1000 money depending on number of enemies and strength of them.
A way I beat Naraku is, I let Sango attack with Kirara(fire cat)when she runs out of spirit energy, I let her attack without spirit energy until she gains it all back. For Miroku I let him do all the healing and reviving.(Do Not use the move to see your opponent's life it'll just come up with ????/???? So don't use it). For Inuyasha, I let him attack with windscar or with ultimate backlash wave(not the normal one)and normal attacks until he gets all his spirit energy back. For Kagome she just highers our attacks and heals. For Shippo, he highers defence. I let my character attack and when she/he's hurt I heal her/him, and do the move that lets you return damage (forgot name of move). Do that and Naraku will eventually die.
If your looking for a dave dpot on Asagiri Island, I found one. All you have to do is when you come to a fork in the road, go north (up). Do that each time you came to a fork, and you will eventually come to one of those cats. THen you can save.